Special Section on Pioneers in Biomedical Optics: Prof. Tayyaba Hasan

How tissue optics affect dosimetry of photodynamic therapy

[+] Author Affiliations
Steven L. Jacques

Oregon Health and Science University, Departments of Dermatology and Biomedical Engineering, Portland, Oregon 97239-4501

J. Biomed. Opt. 15(5), 051608 (October 12, 2010). doi:10.1117/1.3494561
History: Received January 08, 2010; Revised July 10, 2010; Accepted August 17, 2010; Published October 12, 2010; Online October 12, 2010
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We describe three lessons learned about how tissue optics affect the dosimetry of red to near-infrared treatment light during PDT, based on working with Dr. Tayyaba Hasan. Lesson 1—The optical fluence rate ϕ near the tissue surface exceeds the delivered irradiance (E). A broad beam penetrates into tissue to a depth (z) as ϕ=Ekeμz, with an attenuation constant μ and a backscatter term k. In tissues, k is typically in the range 3–5, and 1μ equals δ, the 1e optical penetration depth. Lesson 2—Edge losses at the periphery of a uniform treatment beam extend about 3δ from the beam edge. If the beam diameter exceeds 6δ, then there is a central zone of uniform fluence rate in the tissue. Lesson 3—The depth of treatment is linearly proportional to δ (and the melanin content of pigmented epidermis in skin) while proportional to the logarithm of all other factors, such as irradiance, exposure time, or the photosensitizer properties (concentration, extinction coefficient, quantum yield for oxidizing species). The lessons illustrate how tissue optics play a dominant role in specifying the treatment zone during PDT.

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© 2010 Society of Photo-Optical Instrumentation Engineers

Citation

Steven L. Jacques
"How tissue optics affect dosimetry of photodynamic therapy", J. Biomed. Opt. 15(5), 051608 (October 12, 2010). ; http://dx.doi.org/10.1117/1.3494561


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